If a Field Contains Approximately 1,000 Kilocalories of Energy in Grass

If a field contains approximately 1,000 kilocalories of energy in grass, which is eaten by crickets, which are eaten by birds, then approximately how many kilocalories of energy could be in the birds that live in this field?

A) 1,000
B) 900
C) 100
D) 90
E) 10